1. Field of the Invention
The present invention relates to a protection circuit for an output transistor of a voltage regulator.
2. Description of the Related Art
A related-art voltage regulator is now described. FIG. 6 is a circuit diagram illustrating the related-art voltage regulator.
The related-art voltage regulator includes an error amplifier circuit 104, a reference voltage circuit 103, an NMOS transistor 602, resistors 105 and 106, a diode 601, a ground terminal 100, an output terminal 102, and a power supply terminal 101.
The resistors 105 and 106 are connected in series between the output terminal 102 and the ground terminal 100, and divide an output voltage Vout generated at the output terminal 102. A voltage generated at a connection point of the resistors 105 and 106 is represented by Vfb. The error amplifier circuit 104 controls a gate voltage of the NMOS transistor 602 so that the voltage Vfb may approach a voltage Vref of the reference voltage circuit 103, to thereby control the NMOS transistor 602 to output an output voltage Vout from the output terminal 102. The diode 601 clamps the gate voltage of the NMOS transistor 602 so that the gate of the NMOS transistor is protected from a breakdown even if a voltage exceeding a withstand voltage of the gate of the NMOS transistor is input from the power supply terminal 101 (for example, see Japanese Patent Application Laid-open No. 2002-343874).
However, the related-art voltage regulator has a problem in that, because the gate of the NMOS transistor 602 is clamped by only the diode, a drivability of the NMOS transistor 602 is limited.